The invention relates to a dryer fabric for use in the dryer section of a papermaking machine.
A conventional papermaking machine typically includes a forming section, a press section, and a dryer section wherein the pulp is progressively formed and dried into paper. The different papermaking machine sections require different kinds of papermaking fabric to support and carry the pulp or paper through the particular section. In the dryer section of the papermaking machine, the ability of the dryer fabric to handle water and heat on the machine is of the utmost importance. Typically, fabrics in the dryer section have included woven fabrics or spiral fabrics. These fabrics must be capable of withstanding high temperatures and steam without breaking down. The dryer section includes a number of heated rollers or cylinders. One of the functions of the dryer fabric is to hold the wet paper against the heated cylinder to achieve the dryness desired.
Spiral fabrics which include elongated strips of spirals intermeshing and joined together with pintles are utilized in the dryer section of papermaking machines. For example, spiral papermaking fabrics are disclosed in U.S. Pat. Nos. 4,346,138, 4,381,612, 4,392,902, 4,490,925, and 4,755,420.
The heated cylinders of the dryer section are typically heated by steam introduced into the interior of the cylinders. The operating temperatures are in the range of 100.degree. C.-200.degree. C.
The predominant material for dryer fabrics is polyester. Unfortunately, polyester is susceptible to degradation to an unacceptable extent when operating at the high temperatures and humidity of the dryer section. Fiberglass monofilaments wrapped with acrylic yarns have also been used to form dryer fabrics. They also, to a large extent, have been found to be unsatisfactory because the acrylic tends to carry water, to trap dirt, or become chemically contaminated, all of which results in an unsatisfactory product.
Monofilaments of polyetheretherketone (PEEK) formed into industrial fabrics will function satisfactorily under the high temperature conditions of the dryer section. See U.S. Pat. No. 4,359,501. This material is too costly to manufacture to be economically attractive.
Monofilaments formed from polyphenylene sulphide (PPS) or a blend of PPS and polyamide 66 have also been used to form dryer fabrics. See U.S. Pat. No. 4,755,420. These monofilaments have the draw back that they are brittle and tend to break during the coiling process.
It is an object of this invention to produce a spiral dryer fabric of coiled monofilaments formed of a blend of polyphenylene sulphide (PPS) and fluorocarbon. A well known fluorocarbon is TEFLON.
Another object of this invention is to produce a spiral dryer fabric with superior degradation properties and superior stability properties when exposed to prolonged use under temperatures in the vicinity of 150.degree. C.
Another object of this invention is to produce a coiled dryer fabric using monofilaments having superior toughness and flexibility so as to not sustain breakage during the coiling operation.
Another object of this invention is to produce a dryer fabric for use in at least the first two sections of the dryer section of a paper forming machine.
Another object of this invention is to produce a coiled dryer fabric having the coils formed from monofilaments shaped to have a rectangular cross-section.
Another object of this invention is to produce a coiled dryer fabric having the coils formed from monofilaments shaped to have a circular cross-section.